U.S. patent application number 12/377508 was filed with the patent office on 2010-10-07 for silicone release coating compositions.
Invention is credited to Stephen Cray, Jean De La Croix Habimana, David Rich, Marc Thibaut.
Application Number | 20100255205 12/377508 |
Document ID | / |
Family ID | 37056232 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100255205 |
Kind Code |
A1 |
Cray; Stephen ; et
al. |
October 7, 2010 |
Silicone Release Coating Compositions
Abstract
A release coating composition is prepared comprising a
polyorganosiloxane (A) having alkenyl groups, a crosslinking agent
(B) having organohydrogensiloxane groups, a catalyst for the
hydrosilylation reaction between (A) and (B), and an anchorage
additive for enhancing the adhesion of the composition to a polymer
film substrate. The anchorage additive is the reaction product of a
fluid polyorganosiloxane (C) containing at least one alkenyl group
and at least one silanol group with a hydrolysable silane (D)
containing at least one epoxide group. The curable silicone release
coating composition can be applied to a substrate known as a
`liner` retaining a label, which liner can for example be paper or
a polymer film, and cured.
Inventors: |
Cray; Stephen; (South
Glamorgan, GB) ; Habimana; Jean De La Croix;
(Morlanwelz, BE) ; Rich; David; (South Glamorgan,
GB) ; Thibaut; Marc; (Chapellez Lez Herlaimont,
BE) |
Correspondence
Address: |
HOWARD & HOWARD ATTORNEYS PLLC
450 West Fourth Street
Royal Oak
MI
48067
US
|
Family ID: |
37056232 |
Appl. No.: |
12/377508 |
Filed: |
August 2, 2007 |
PCT Filed: |
August 2, 2007 |
PCT NO: |
PCT/EP07/58022 |
371 Date: |
June 16, 2010 |
Current U.S.
Class: |
427/386 ;
524/506 |
Current CPC
Class: |
C09D 183/06 20130101;
C08K 5/541 20130101; C08L 83/06 20130101; C08L 83/00 20130101; C08K
5/541 20130101; C08L 83/04 20130101; C08L 83/06 20130101 |
Class at
Publication: |
427/386 ;
524/506 |
International
Class: |
B05D 3/02 20060101
B05D003/02; C09D 183/07 20060101 C09D183/07 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 2006 |
GB |
GB 0616021.2 |
Aug 2, 2007 |
EP |
PCT/EP2007/058022 |
Claims
1. A release coating composition comprising a polyorganosiloxane
(A) having alkenyl groups, a crosslinking agent (B) having
organohydrogensiloxane groups, a catalyst for the hydrosilylation
reaction between (A) and (B), and an anchorage additive for
enhancing the adhesion of the composition to a polymer film
substrate, characterised in that the anchorage additive is the
reaction product of a fluid polyorganosiloxane (C) containing at
least one alkenyl group and at least one silanol group with a
hydrolysable silane (D) containing at least one epoxide group.
2. A release coating composition according to claim 1,
characterised in that the polyorganosiloxane (C) has a degree of
polymerisation of at 4 to 50 siloxane units.
3. A release coating composition according to claim 1,
characterised in that the polyorganosiloxane (C) is a
polydiorganosiloxane having terminal silanol groups.
4. A release coating composition according to claim 3,
characterised in that the polyorganosiloxane (C) is a copolymer of
methylvinylsiloxane units and dimethylsiloxane units.
5. A release coating composition according to claim 1,
characterised in that the silane (D) comprises an
(epoxy-substituted alkyl) di or trialkoxy silane.
6. A release coating composition according to claim 1,
characterised in that the epoxide groups in the silane (D) are
present as glycidyl groups.
7. A release coating composition according to claim 1,
characterised in that the epoxide groups in the silane (D) are
epoxycyclohexyl groups.
8. A release coating composition according to claim 1,
characterised in that the fluid polyorganosiloxane (C) and
hydrolysable silane (D) are reacted in a weight ratio in the range
10:90 to 90:10.
9. A release coating composition according to claim 1,
characterised in that the anchorage additive is the reaction
product of the polyorganosiloxane (C), the silane (D) and a
di(hydrocarbyl)dialkoxysilane in which each hydrocarbyl group is
selected from alkyl and alkenyl groups.
10. A release coating composition according to claim 1,
characterised in that the polyorganosiloxane (A) is a branched
siloxane comprising one or more Q units of the formula
(SiO.sub.4/2), from 15 to 995 D units of the formula
R.sup.b2SiO2.sub./2 and M units of the formula
R.sup.aR.sup.b.sub.2SiO.sub.1/2, wherein the R.sup.a and R.sup.b
substituents are selected from alkyl and alkenyl groups having 1 to
6 carbon atoms, at least three R.sup.a substituents in the branched
siloxane being alkenyl units.
11. A release coating composition according to claim 1,
characterised in that the composition further contains a cure
inhibitor selected from ethylenically or aromatically unsaturated
amides, acetylenic compounds, ethylenically unsaturated
isocyanates, olefinic siloxanes, unsaturated hydrocarbon diesters,
conjugated ene-ynes, hydroperoxides, nitriles and diaziridines.
12. A release coating composition according to claim 1,
characterised in that the anchorage additive is present at 0.5 to
10% by weight of the release coating composition.
13. A process for providing a release coating to a polymer film
comprising applying to the polymer film a composition comprising a
polyorganosiloxane (A) having alkenyl groups, a crosslinking agent
(B) having organohydrogensiloxane groups, a catalyst for the
hydrosilylation reaction between (A) and (B) and an anchorage
additive for enhancing the adhesion of the composition to the
polymer film and heating the coated film to cure the release
coating, characterised in that the anchorage additive is the
reaction product of a fluid polyorganosiloxane (C) containing at
least one alkenyl group and at least one silanol group with a
hydrolysable silane (D) containing at least one epoxide group.
14. (canceled)
15. A release coating composition according to claim 2,
characterised in that the polyorganosiloxane (C) is a
polydiorganosiloxane having terminal silanol groups.
16. A release coating composition according to claim 15,
characterised in that the polyorganosiloxane (C) is a copolymer of
methylvinylsiloxane units and dimethylsiloxane units.
17. A release coating composition according to claim 2,
characterised in that the silane (D) comprises an
(epoxy-substituted alkyl) di or trialkoxy silane.
18. A release coating composition according to claim 2,
characterised in that the epoxide groups in the silane (D) are
present as glycidyl groups.
19. A release coating composition according to claim 2,
characterised in that the epoxide groups in the silane (D) are
epoxycyclohexyl groups.
Description
[0001] This invention relates to curable silicone release coating
compositions. Silicone based release coatings are useful in
applications where relatively non-adhesive surfaces are required.
The curable silicone release coating composition is applied to a
substrate known as a `liner`, which can for example be paper or a
polymer film, and cured. Single-sided liners, for example, backing
sheets for pressure sensitive adhesive labels, are used to
temporarily retain the labels without affecting the adhesive
properties of the labels. Double-sided liners, for example
interleaving papers for double-sided and transfer tapes, are used
to ensure the protection and desired unwind characteristics of a
double-sided self-adhesive tape or adhesive film. The release
coating is required to adhere well to the liner while having
relatively low adhesion to the adhesive so that the label can be
removed from the liner by a predetermined peel force. The present
invention relates to curable silicone release coating compositions
which adhere well to a wide variety of liner substrates, and in
particular have improved adhesion to polymer substrates such as
polyester films.
[0002] A liner substrate is coated by applying a silicone based
release coating composition onto the substrate and subsequently
curing the composition. The preferred curing mechanism is thermally
initiated hydrosilylation, which can readily be modified to vary
the adhesive force between the release coating and the adhesive
label. The basic constituents of silicone based release coating
compositions which are cured by hydrosilylation are (A) a
polyorganosiloxane containing alkenyl groups, (B) a cross-linking
agent containing organohydrogensiloxane groups and a catalyst for
the hydrosilylation reaction between (A) and (B).
[0003] The liner substrate to which the release coating is applied
is usually paper, but there is an increasing requirement for
release coating of polymer substrates such as polyester, for
example polyethylene terephthalate, film, polypropylene or
polyethylene, particularly for clear on clear labels. Although the
smooth surface of films has desired benefits in reduced transfer of
adhesive patterns to the label, the use of film substrates, in
particular unprimed polyester film, has the disadvantage of showing
greater tendency of the silicone to rub off over time. After a few
days at room temperature, the silicone layer may become easily
removed from the polymeric film by simply rubbing with a finger.
The use of polyethylene, polypropylene and polyester film liners
has led to the need to design silicone release coatings with
improved anchorage and delayed rub-off performance.
[0004] WO-A-2004/046267 describes a release coating composition
comprising a siloxane (A) having alkenyl groups, a crosslinking
agent (B) having organohydrogensiloxane groups and a catalyst for
the hydrosilylation reaction between (A) and (B), additionally
containing a polydiorganosiloxane of viscosity 10-200000 mPas at
25.degree. C. consisting essentially of diorganosiloxane units of
the formula --(SiR.sub.2--O)-- in which each R group is an alkyl
group having 1 to 4 carbon atoms, to improve anchorage of the
release coating on polymer film. The composition may contain a
further adhesion improving additive such as an epoxysilane, a
silanol-terminated polydiorganosiloxane containing at least one
alkenyl group, or a melamine resin.
[0005] US-A-2003/0088042 describes a release coating composition,
comprising (A) an anchorage additive which is the reaction product
of a vinyl alkoxysilane, an epoxy-functional alkoxysilane, a
catalyst and water, (B) an alkenyl silicone, (C) a hydrogen
siloxane, (D) a hydrosilylation catalyst and (E) a cure
inhibitor.
[0006] US-A-2004/0254274 and corresponding WO-A-2005/000983
describes additives for improved anchorage of silicone pressure
sensitive adhesive composition coatings comprising
(R.sub.aSiO.sub.(4-a)/2).sub.n where n is an integer greater than
3, a is from 1 to 3, R is a silicon-hydride and or an
alkylenealkoxysilyl containing organic radical, with at least one
silicon-hydride and one alkylenealkoxysilyl containing radical
being present on the molecule. US2005/0038188A1 describes a
composition prepared by mixing components comprising: (I) a
polyorganosiloxane having an average of at least two unsaturated
organic groups per molecule, optionally (II) an
organohydrogenpolysiloxane having an average of at least two
silicon-bonded hydrogen atoms per molecule, (III) a hydrosilylation
catalyst; (IV) a fluoroorganosilicone; and (V) an adhesion
promoter. Components (I) and (II) are free of fluorine atoms.
Component (IV) has at least one functional group reactive with
component (I), component (II), or both. When component (II) is not
present, the component (IV) has an average of at least two
silicon-bonded hydrogen atoms per molecule. Components (IV) and (V)
are present in amounts sufficient to improve resistance to Bleed.
Component (V) may comprise an epoxy-functional siloxane such as a
physical blend or a reaction product of a hydroxy-terminated
polyorganosiloxane with an epoxy-functional alkoxysilane. The
compositions are adhesives and are used as die attach adhesives
used in electronic applications. These compositions contain
fillers, typically 1% by weight fumed silica treated with
hexamethyldisilazane and 60% by weight of spherical fused
silica.
[0007] EP 0 556 023 A1 describes epoxy methylsiloxanes as anchorage
additives for heat curable solventless addition cured paper release
compositions resulting from platinum catalyzed hydrosilation of
alkenyl siloxanes and silicon hydride siloxanes.
[0008] WO 2003/03578 describes a liquid silicone formulation, for
use as a coating base for high-speed production of crosslinked
release and water repellent elastomer coating on a solid support,
which comprises at least a crosslinkable polyorganosiloxane POS
(I), (SiVi-type POS and SiH-type POS); at least a (platinum-based)
catalyst (ii); optionally an adherence modulator system (III); an
adherence promoter (IV) comprising an epoxidized alkoxysilane
and/or an alkenylated alkoxysilane, as well as a metal chelate
and/or a metal alkoxide (GLYMO/MEMO/TiO4Bu).
[0009] There is a need for release coating compositions comprising
an anchorage additive that shows more reliable adhesion of curable
silicone release coating compositions onto all substrates,
especially polymer films including commercial unprimed polyester
with or without preliminary surface treatment.
[0010] A release coating composition according to the invention
comprises a polyorganosiloxane (A) having alkenyl groups, a
crosslinking agent (B) having organohydrogensiloxane groups, a
catalyst for the hydrosilylation reaction between (A) and (B), and
an anchorage additive for enhancing the adhesion of the composition
to a polymer film substrate, characterised in that the anchorage
additive is the reaction product of a fluid polyorganosiloxane (C)
containing at least one alkenyl group and at least one silanol
group with a hydrolysable silane (D) containing at least one
epoxide group.
[0011] The invention includes a process for providing a release
coating to a polymer film comprising applying to the polymer film a
composition comprising a polyorganosiloxane (A) having alkenyl
groups, a crosslinking agent (B) having organohydrogensiloxane
groups, a catalyst for the hydrosilylation reaction between (A) and
(B) and an anchorage additive for enhancing the adhesion of the
composition to the polymer film and heating the coated film to cure
the release coating, characterised in that the anchorage additive
is the reaction product of a fluid polyorganosiloxane (C)
containing at least one alkenyl group and at least one silanol
group with a hydrolysable silane (D) containing at least one
epoxide group.
[0012] According to a further aspect, the invention includes the
use of the reaction product of a fluid polyorganosiloxane (C)
containing at least one alkenyl group and at least one silanol
group with a hydrolysable silane (D) containing at least one
epoxide group in a release coating composition comprising a
polyorganosiloxane (A) having alkenyl groups, a crosslinking agent
(B) having organohydrogensiloxane groups and a catalyst for the
hydrosilylation reaction between (A) and (B) as an anchorage
additive for enhancing the adhesion of the composition to a polymer
film substrate.
[0013] The siloxane (A) is an organopolysiloxane having at least
two silicon-bonded alkenyl-functional groups per molecule. The
alkenyl group is preferably linear having up to 6 carbon atoms, as
exemplified by hexenyl, vinyl, allyl or pentenyl, or may be
cycloalkenyl such as cyclohexenyl.
[0014] (A) can for example be a linear organopolysiloxane having
the general formula
YX.sub.2SiO(X.sub.2SiO).sub.x(XZSiO).sub.ySiX.sub.2Y
wherein each X denotes independently a phenyl group or an alkyl or
cycloalkyl group having from 1 to 10 carbon atoms, for example,
methyl, ethyl, propyl, butyl or cyclohexyl; each Y and Z denotes an
alkenyl group; and X and Y are such that (A) has a viscosity at
25.degree. C. is in the range from 50 to 5000 mm.sup.2/s, most
preferably 200 to 500 mm.sup.2/s. At least 90% of all the X
substituents of (A) are preferably methyl groups, most preferably
all being methyl groups. It is preferred that no more than 4% of
all units of (A) organopolysiloxane are units with an alkenyl
group, as otherwise there is the possibility of crosslinking the
release coating composition too much upon curing. Preferably y=0.
It is possible but not preferred that small amounts (preferably
less than 2% of all the substituents present) of other substituents
are present, for example hydroxyl groups.
[0015] One preferred siloxane (A) is a branched siloxane comprising
one or more Q units of the formula (SiO.sub.4/2), from 15 to 995 D
units of the formula R.sup.b.sub.2SiO.sub.2/2 and M units of the
formula R.sup.aR.sup.b.sub.2SiO.sub.1/2, wherein the R.sup.a and
R.sup.b substituents are selected from alkyl and alkenyl groups
having 1 to 6 carbon atoms, at least three R.sup.a substituents in
the branched siloxane being alkenyl units, as described in
EP-A-1070734. Such a siloxane may for example be a
poly(dimethylsiloxane-silicate) copolymer having at least three
vinyldimethylsilyl-terminated siloxane branches. The branched
siloxane can also incorporate other terminal groups such as
terminal trimethylsilyl (SiMe.sub.3) and/or terminal
hydroxydimethylsilyl (SiMe.sub.2OH) groups. This so-called Q
branched siloxane can contain other additional branching groups,
for example it can also incorporate T.sup.Vi units, of the formula
ViSiO.sub.3/2 where Vi denotes a vinyl group, within the chain
without affecting the anchorage. Branched siloxanes have the
advantage that they allow faster cure than linear polymers with
similar viscosities. Release coating compositions based on such
branched siloxanes develop good anchorage when combined with the
anchorage additives of this invention.
[0016] The organohydrogenpolysiloxane crosslinking agent (B)
generally contains at least three Si--H groups and may have the
general formula:--
R.sup.t.sub.3SiO.sub.1/2((CH.sub.3).sub.2SiO.sub.2/2).sub.d(R.sup.t.sub.-
2SiO.sub.2/2).sub.e)SiO.sub.1/2R.sup.t.sub.3
where each R.sup.t may be an alkyl group having 1 to 4 carbon atoms
or hydrogen, d is 0 or an integer, e is an integer such that d+e is
from 8 to 400. Alternatively the cross-linking agent may be an MQ
resin consisting of units of the general formula SiO.sub.4/2 and
R.sup.q.sub.3SiO.sub.1/2 wherein at least three R.sup.q
substituents are hydrogen atoms and the remainder are alkyl groups,
or may be a rake or comb polymer comprising a polydiorganosiloxane
chain containing one or more T (having the general formula
R.sup.bSiO.sub.3/2) or Q units having a subchain of
diorganosiloxane units attached thereto via oxygen. It is preferred
that the hydrosiloxane crosslinker has a viscosity of from 5 to
1000 mm.sup.2/s at 25.degree. C., more preferably 20 to 350
mm.sup.2/s, most preferably 50 to 300 mm.sup.2/s. The crosslinking
agent (B) is preferably present in an amount such that the molar
ratio of the total number of Si--H groups in the release coating
composition to alkenyl groups in the composition is from 0.9:1 to
8:1, more preferably 1.1:1 to 4:1, most preferably 1.5:1 to
3:1.
[0017] Suitable hydrosilylation catalysts include complexes or
compounds of group VIII metals, for example, platinum, ruthenium,
rhodium, palladium, osmium and indium. Preferred catalysts are
platinum compounds or complexes including chloroplatinic acid,
platinum acetylacetonate, complexes of platinous halides with
unsaturated compounds, for example, ethylene, propylene,
organovinylsiloxanes and styrene, hexamethyldiplatinum,
PtCl.sub.2.PtCl.sub.3 and Pt(CN).sub.3. Alternatively the catalyst
may be a rhodium complex, for example, RhCl.sub.3(Bu.sub.2S).sub.3.
The catalyst is typically used at 40 to 250 parts per million by
weight platinum (or other group VIII metal) based on the weight of
the release coating composition.
[0018] The fluid polyorganosiloxane (C) used in the preparation of
the anchorage additive generally contains at least one alkenyl
group and at least one silanol group. The polyorganosiloxane (C)
generally contains a chain of at least 3 siloxane units and is
preferably a substantially linear polydiorganosiloxane. The
polyorganosiloxane (C) preferably has a degree of polymerisation of
at least 4 and preferably at least 6 siloxane units up to 30, 50 or
100 siloxane units. The polyorganosiloxane (C) can for example have
a viscosity in the range 2 to 200 mm.sup.2/s at 25.degree. C. The
alkenyl group can for example have from 2 to 6 carbon atoms, for
example a vinyl or 5-hexenyl group. The polyorganosiloxane (C)
usually also contains alkyl groups, particularly alkyl groups
having 1 to 4 carbon atoms such as methyl or ethyl groups and may
contain aryl groups such as phenyl. The alkenyl groups can be
present as pendant groups, for example the copolymer (C) can be a
polymethylvinylsiloxane, or a copolymer of methylvinylsiloxane
units and dimethylsiloxane units, or a copolymer of divinylsiloxane
units and dimethylsiloxane units. Alternatively or additionally the
alkenyl groups can be present as terminal groups, for example in
methylvinylsilanol terminal units. The silanol groups are
preferably present in terminal units such as dimethylsilanol or
methylvinylsilanol terminal units. Most preferably the
polyorganosiloxane (C) is a polydiorganosiloxane having terminal
silanol groups at both ends of the siloxane chain, although part or
all of the polyorganosiloxane (C) may have one silanol end group
and one Si-alkoxy end group, for example a dimethylmethoxysilyl end
unit. The polyorganosiloxane (C) can for example be formed by the
reaction of methylvinyldimethoxysilane and dimethyldimethoxysilane
in the presence of a silane hydrolysis catalyst such as a base or
an acid.
[0019] The hydrolysable silane (D) which is reacted with the
polyorganosiloxane (C) to form the anchorage additive generally
contains at least one epoxide group per molecule. The epoxide group
can for example be present as a glycidyl group or a
3,4-epoxycyclohexyl group. The silane (D) can for example be of the
formula (R*).sub.e(R'').sub.fSi(OA).sub.(4-e-f), where R*
represents a substituted alkyl group containing an epoxide group,
R'' represents an alkyl group preferably having 1 to 6 carbon atoms
such as a methyl or ethyl group, A represents an alkyl group having
1 to 4 carbon atoms such as a methyl or ethyl group, e is 1, 2 or
3, most preferably 1, and f is 0, 1 or 2, most preferably 0 or 1.
The group R* can for example be a 3-glycidoxypropyl, glycidyl,
5,6-epoxyhexyl, 3,4-epoxycyclohexyl, 2-(3,4-epoxycyclohexyl)ethyl,
3-(3,4-epoxycyclohexyl)propyl or 3,4-epoxycyclohexylmethyl group.
Examples of suitable hydrolysable silanes (D) include
3-glycidoxypropyltrimethoxysilane,
3-glycidoxypropyltriethoxysilane,
methyl(3-glycidoxypropyl)dimethoxysilane,
methyl(3-glycidoxypropyl)diethoxysilane,
2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and
3-(3,4-epoxycyclohexyl)propyltrimethoxysilane.
[0020] The fluid polyorganosiloxane (C) and the hydrolysable silane
(D) can be reacted at elevated temperature and/or in the presence
of a silanol condensation catalyst. The catalyst can for example be
a base such as potassium hydroxide, sodium hydroxide, potassium
silanolate or a phosphazene base, or can be an acid such as HCl, or
can be a titanate ester or an organic compound of tin. The
temperature of reaction is preferably in the range 50 to
150.degree. C. The novel anchorage additive thus prepared generally
contains at least one epoxy group, at least one alkenyl group and
at least one alkoxy group in its molecule.
[0021] The fluid polyorganosiloxane (C) and the hydrolysable silane
(D) are preferably reacted at 0.5 to 1.5 moles silane (D) per
silanol group of fluid polyorganosiloxane (C). The weight ratio of
fluid polyorganosiloxane (C) to hydrolysable silane (D) will vary
according to the chain length of fluid polyorganosiloxane (C), but
is usually in the range 25:75 to 95:5, particularly 40:60 to
90:10
[0022] The fluid polyorganosiloxane (C) and the hydrolysable silane
(D) can if desired be co-reacted with a dialkyldialkoxysilane such
as dimethyldimethoxysilane and/or with an alkenyl dialkoxysilane
such as methylvinyldimethoxysilane. Such a diorganodialkoxysilane
reacts as a chain extender for the siloxane chains of the fluid
polyorganosiloxane (C) while still allowing reaction with the
epoxide functional hydrolysable silane (D).
[0023] The extent of reaction between the fluid polyorganosiloxane
(C) and the hydrolysable silane (D) is preferably sufficient that
at least 50%, and preferably at least 80%, of the hydrolysable
epoxy-functional silane (D) is present in the anchorage additive as
reaction product rather than as unreacted silane. We have found
that the reaction product when used as anchorage additive has
better compatibility with the other components of the silicone
release coating than the hydrolysable epoxy-functional silane (D)
and (whether or not (D) is used with additional hydrolysable vinyl
silane or siloxane) leads to more consistent anchorage to polymer
film substrates. The hydrolysable epoxy-functional silane (D) has
some tendency to self-condense when the silicone release coating
composition is cured, forming siloxane resin of reduced
compatibility with the cure product of polyorganosiloxane (A) and
crosslinking agent (B).
[0024] We believe that the presence in the reaction product of
siloxane chains derived from the fluid polyorganosiloxane (C) leads
to better compatibility with the other components of the silicone
release coating and may give more consistent anchorage to polymer
film substrates than a reaction product of the hydrolysable
epoxy-functional silane (D) with a vinyltrialkoxysilane.
[0025] The anchorage additive is preferably present in the release
coating at 0.1 to 20% by weight of the siloxane content of the
coating, for example at 0.5 to 5 or 10% by weight.
[0026] The release coating composition is preferably substantially
solventless, but can alternatively be a solution in an organic
solvent, for example a solution in a hydrocarbon solvent such as
xylene or toluene, or an aqueous emulsion stabilised by a nonionic,
anionic or cationic surfactant. A solution or emulsion can for
example have a concentration of for example 4 to 50% by weight.
Preferably the release coating composition has a viscosity of not
less than 50 mm.sup.2/s and not more than 10000 mm.sup.2/s at
25.degree. C.; more preferably the viscosity is from 50 to 1000
mm.sup.2/s.
[0027] The composition may additionally comprise one or more cure
inhibitors adapted to prevent the cure of the coating composition
from occurring below a predetermined temperature. A cure inhibitor
may be effective to delay or prevent the room temperature cure of
the silicone composition to provide a long coating operation time
without compromising the cure rate at elevated temperature. Such an
inhibitor is often used in silicone release coatings which cure by
hydrosilylation and may be used in the compositions according to
the present invention, although an inhibitor may not be necessary
at the lower levels of platinum metal catalyst. The inhibitor can
be any material that is known to be, or can be, used to inhibit the
catalytic activity of platinum group metal-containing catalysts.
Examples of suitable inhibitors include ethylenically or
aromatically unsaturated amides, acetylenic compounds, silylated
acetylenic compounds, ethylenically unsaturated isocyanates,
olefinic siloxanes, unsaturated hydrocarbon monoesters and
diesters, conjugated ene-ynes, hydroperoxides, nitriles, and
diaziridines. [0016] Typical inhibitors include acetylenic alcohols
exemplified by 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol,
2-phenyl-3-butyn-2-ol, 2-ethynyl-isopropanol,
2-ethynyl-butane-2-ol, and 3,5-dimethyl-1-hexyn-3-ol, silylated
acetylenic alcohols exemplified by trimethyl
(3,5-dimethyl-1-hexyn-3-oxy)silane,
dimethyl-bis-(3-methyl-1-butyn-oxy)silane,
methylvinylbis(3-methyl-1-butyn-3-oxy)silane, and
((1,1-dimethyl-2-propynyl)oxy)trimethylsilane, unsaturated
carboxylic esters exemplified by diallyl maleate, dimethyl maleate,
diethyl fumarate, diallyl fumarate, and
bis-2-methoxy-1-methylethylmaleate, mono-octylmaleate,
mono-isooctylmaleate, mono-allyl maleate, mono-methyl maleate,
mono-ethyl fumarate, mono-allyl fumarate,
2-methoxy-1-methylethylmaleate; and a fumarate/alcohol mixture
wherein the alcohol is, for example, benzyl alcohol or 1-octanol
and ethenyl cyclohexyl-1-ol, conjugated ene-ynes exemplified by
2-isobutyl-1-butene-3-yne, 3,5-dimethyl-3-hexene-1-yne,
3-methyl-3-pentene-1-yne, 3-methyl-3-hexene-1-yne,
1-ethynylcyclohexene, 3-ethyl-3-butene-1-yne, and
3-phenyl-3-butene-1-yne, vinylcyclosiloxanes such as
I,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, and a
mixture of a conjugated ene-yne as described above and a
vinylcyclosiloxane as described above. Typically the inhibitors are
diallyl maleate, bis-2-methoxy-1-methylethylmaleate,
1-ethynyl-1-cyclohexanol, and 3,5-dimethyl-1-hexyn-3-ol. If used,
an inhibitor can for example be used at 0.1 to 3% by weight of the
release coating composition.
[0028] The release coating composition may contain a release
modifier in order to control (increase) the level of release force
(the adhesive force between the release coating and the adhesive
label). Release coating compositions having the required release
force can be formulated from a premium (modifier-free) release
coating composition by adjusting the level of modifier. The release
modifier is usually packaged as a separate component so that the
amount of modifier added to the release coating composition can be
controlled. The release modifier package may also contain the
anchorage additive reaction product of (C) and (D). Any appropriate
silicone release modifier may be used. Examples include an
alkenylated silicone resin, an alkenylated polydiorganosiloxane,
one or more primary alkenes containing from 12 to 30 carbon atoms,
and/or one or more branched alkenes containing at least 10 carbon
atoms. If used, a release modifier can for example be used at up to
85% by weight, often 25 to 85%, based on the polyorganosiloxane
(A).
[0029] Other constituents which may also be added to release
coating compositions of the present invention include, for example,
bath life extenders such as an alcohol, reactive diluents,
fragrances, preservatives and fillers, for example, silica, quartz
or chalk.
[0030] The release coating composition according to the invention
preferably is free of filler or contains only a limited amount of
filler, typically from 0 to 30% by weight of the composition.
Fillers can agglomerate or otherwise stick to the coater equipment
used to apply the release coating. They can hinder optical
properties, for example transparency, of the release coating and of
the final label. The fillers may be prejudicial to the adherence of
the label.
[0031] A release coating composition according to the invention
preferably comprises a polyorganosiloxane (A) having alkenyl
groups, a crosslinking agent (B) having organohydrogensiloxane
groups, a catalyst for the hydrosilylation reaction between (A) and
(B), an anchorage additive for enhancing the adhesion of the
composition to a polymer film substrate, and from 0 to 30% by
weight of the composition is formed of spherical fused silica,
characterised in that the anchorage additive is the reaction
product of a fluid polyorganosiloxane (C) containing at least one
alkenyl group and at least one silanol group with a hydrolysable
silane (D) containing at least one epoxide group. Preferably, the
composition contains less than 25%, less than 10%, less than 5%,
preferably less than 1% of spherical fused silica. Preferably, the
composition contains no or less than 25%, less than 10%, less than
5%, preferably less than 1% of filler.
[0032] The release coating composition of the invention is
preferably free from fluoroorganosilicone compound. It is believed
that, during the cure, a fluorocompound, because of its low surface
tension, will rapidly migrate to the interface coating/substrate,
for example a PET film/silicone coating interface, and prevent
bleeding by making a fluorine containing barrier. By making a
barrier, it prevents any component from reacting at the interface,
thus if this system is used as release coating, the fluorocompound
will pull the anchorage additive AA at the air/silicone interface
instead of pulling it at the PET film/silicone interface. Even in
case it could drag an anchorage additive to the right interface, it
will make a barrier there, preventing further contact between AA
and the film surface, impeding bonding the silicone coating to the
polymer film substrate. Moreover, fluorosilicone compounds are
usually expensive.
[0033] While release coating compositions of the present invention
may be prepared by merely premixing the constituents together, it
may be more desirable to prepare such compositions in separate
parts or packages to be combined at the time the composition is
applied as a coating. The packages can for example be: [0034] (i) a
first part comprising the alkenyl siloxane (A) and inhibitor, a
second part comprising a release modifier and inhibitor, a third
part comprising the catalyst and a fourth part comprising the
cross-linking agent (B); or [0035] (ii) a first part comprising the
alkenyl siloxane (A) and catalyst, a second part comprising a
release modifier and the catalyst and a third part comprising the
cross-linking agent (B) and inhibitor.
[0036] The anchorage additive can be incorporated in any one or
more of these packages or be added to the coating bath as a
separate component. For example the anchorage additive can be mixed
with the alkenyl siloxane (A) or can alternatively or additionally
be mixed with the release modifier.
[0037] The release coating composition of the invention can be
applied to any substrate but is particularly effective on
substrates where anchorage is a problem, such as polymer film
substrates, for example polyester, particularly polyethylene
terephthalate (PET), polyethylene, polypropylene, or polystyrene
films, including oriented and biaxially oriented films, for example
biaxially oriented polypropylene. The release coating composition
can alternatively be applied to a paper substrate, including
plastic coated paper, for example paper coated with polyethylene,
where anchorage may be a problem.
[0038] It may be preferred to expose a polymer film substrate to a
corona discharge before the release coating is applied. Although
the silicone release coating of the invention has improved
anchorage even without corona discharge treatment, in certain
instances the anchorage may be further improved if the film is
corona treated before coating. Many customers for release coatings
want to be able to coat any polyester film. For most polyester
films, the silicone release coating of the invention has excellent
anchorage even without corona discharge. Corona treatment in some
cases will further improve the anchorage of the silicone coating to
the substrate. The use of the anchorage additive of this invention
avoids the need to treat a polyester film surface with primers
before applying the release coating. Corona treatment can for
example be carried out just before coating the film. The corona
discharge station can be incorporated as a pre-treatment in the
film coating apparatus.
[0039] The release coating can for example be applied to the
polymer substrate by spraying, doctor blade, dipping, screen
printing or by a roll coater, e.g. an offset web coater, kiss
coater or etched cylinder coater.
[0040] After application, the release coating is cured on the
polymer film at a temperature of 70-180.degree. C., preferably
100-160.degree. C. The new anchorage additive does not affect the
temperature at which the coating cures. Under production coater
conditions cure can be affected in a residence time of 1 second to
6 seconds, preferably from 1.5 seconds to 3 seconds, at an air
temperature of 120-150.degree. C. Heating can be carried out in an
oven, e.g. an air circulation oven or tunnel furnace or by passing
the coated film around heated cylinders.
[0041] The invention is illustrated by the following detailed
Examples, in which parts and percentages are by weight and all
viscosities were measured at 25.degree. C.
EXAMPLE 1
[0042] 80% by weight of a silanol-terminated methylvinylsiloxane
dimethylsiloxane copolymer with a viscosity of 20 mm.sup.2/s,
comprising mainly {acute over (.alpha.)},.omega.-hydroxy-terminated
siloxane with some {acute over
(.alpha.)}-hydroxy-.omega.-methoxy-terminated siloxane, was reacted
with 20% 3-glycidoxypropyltrimethoxysilane in the presence of
potassium silanolate at 100.degree. C. for an hour to produce a
reaction product (ARP) containing at least one epoxy group, at
least one alkenyl group and at least one alkoxy group in its
molecule. At least 80% of the epoxy groups from the
glycidoxypropyltrimethoxysilane were incorporated in the anchorage
additive reaction product which also contained siloxane chains from
the silanol-terminated polysiloxane.
[0043] A mixed trimethylsilyl, vinyldimethylsilyl-terminated
poly(dimethylsiloxane-silicate) copolymer QBP of DP about 250 was
mixed with diallyl maleate (DAM) inhibitor and ARP anchorage
additive as described above. The resulting mix was then mixed with
poly(methylhydrogen)siloxane crosslinker (MHS) and a
hydrosilylation catalyst (CAT) which is the reaction product of
chloroplatinic acid and divinyltetramethyldisiloxane (0.5% Pt).
[0044] The release coating composition thus produced was coated
onto unprimed polyester film (sold under the Trade Mark TORAY
TERPHANE 60.01) by a blade coater and oven cured at 140.degree. C.
for a dwell time of 3 seconds, and was laminated with an emulsion
acrylic adhesive. Coating experiments were carried out both on film
that had been corona treated (Example 1A) and on film that had not
been corona treated (Example 1B).
[0045] The laminate was stored for 47 weeks and anchorage was
tested by rubbing a finger firmly over the release coated film back
and forth for 10 cycles, and determining if any of the coating had
been damaged or removed. The results are listed in Table 1 as
N N N=No smear, no migration, no rub off VSRO=Very slight rub
off
SRO=Slight rub off
RO=Rub off
[0046] GRO=gross rub off
[0047] In a comparative example, Example 1 was repeated replacing
the anchorage additive ARP by a cold blend (CBL) of 80%
silanol-terminated methylvinylsiloxane dimethylsiloxane copolymer
used in Example 1 and 20% 3-glycidoxypropyltrimethoxysilane. The
results of the comparative example are also shown in Table 1.
TABLE-US-00001 TABLE 1 QBP DAM ARP CBL MHS CAT Rub-off Ex 1A 96.4
0.60 3 4.16 2.4 NNN Ex 1B 96.4 0.60 3 4.16 2.4 NNN Comp Ex A 96.4
0.60 3 4.16 2.4 RO Comp Ex B 96.4 0.60 3 4.16 2.4 GRO
EXAMPLE 2
[0048] 233 gr of trimethylsilyl, vinyldimethylsilyl-terminated
poly(dimethylsiloxane-silicate) copolymer of viscosity 450 mP.s was
blended with 10.8 gr poly(methylhydrogen)siloxane crosslinker MHS
(SiH to vinyl molar ratio 3:1), 39.5 gr vinyl-functional silicone
resin containing Sia.sub.4/2 units as release modifier, 1.5 gr
diallyl maleate, 7.1 gr of the catalyst CAT used in Example 1
giving a platinum level of 120 parts per million (ppm) and 5.2 gr
of the anchorage additive ARP of Example 1.
[0049] After blending, the prepared release coating was coated on
`Toray Terphane 60.01` PET film of 30 micron using 3 rolls reverse
gravure coating head at 18 m/min. It was cured for 3 sec at
140.degree. C. using a 11 KW hot air drying oven. An acrylic
emulsion adhesive sold by BASF under the Trade Mark V210 was coated
over the cured silicone release coating using a bar coater and then
dried at 150.degree. C. for 30 sec in a static oven from Selecta.
After drying, the siliconised, adhesive coated film was laminated
with 50 micron PET sold under the Trade Mark `Jindal 400` using a
hot roll laminator from Chem. Instruments. The laminated samples
were aged in a humidity chamber at 65.degree. C./85% RH. The
anchorage was measured by rubbing off the silicone with a finger.
There was no rub-off initially, or after storage for 1, 2, 4, 8, 16
or 31 days.
EXAMPLES 3 TO 10 AND COMPARATIVE EXAMPLES C2A TO C2D
[0050] Example 2 was repeated varying the amount of anchorage
additive and/or catalyst in the release coating composition, and/or
varying the SiH/vinyl ratio by varying the amount of crosslinker
MHS, and/or varying the dwell time in the oven, as shown in Table
2. The coating procedure was also varied in that the film coated
with release coating was treated in situ with 70 watt m.sup.-2
min.sup.-1 of corona discharge, and the cure temperature was
150.degree. C. in all of Examples 3 to 10 and C2A to C2D.
TABLE-US-00002 TABLE 2 % Anchorage Example Additive Dwell Time (s)
Platinum ppm SiH/SiVi 3 5 1.6 120 2 C2A 0 2.4 120 2 C2B 0 2.4 80 4
4 2.5 2 100 3 5 5 1.6 80 4 6 2.5 2 100 3 C2C 0 1.6 120 4 7 2.5 2
100 3 8 5 2.4 80 2 9 5 2.4 120 4 C2D 0 1.6 80 2 10 2.5 2 100 3
[0051] The anchorage levels of the release coatings of all of
Examples 3 to 10 and C2 to C5 were measured by rubbing each film
with a finger after 0, 2, 5, 7 and 14 days ageing. The results are
shown in Table 3
TABLE-US-00003 TABLE 3 Days at 65.degree. C./85% RH Example 0 2 5 7
14 3 SRO NNN VSRO NNN VSRO C2A VSRO0 GRO GRO GRO GRO C2B NNN GRO
GRO GRO GRO 4 NNN NNN NNN NNN NNN 5 SRO SRO VSRO NNN NNN 6 NNN NNN
NNN NNN NNN C2C NNN GRO GRO GRO GRO 7 NNN NNN NNN NNN NNN 8 SRO
VSRO VSRO NNN NNN 9 NNN NNN NNN NNN NNN C2D NNN GRO GRO GRO GRO 10
NNN NNN NNN NNN NNN
[0052] Table 3 shows that the level of anchorage drops down rapidly
when there is no anchorage additive in the formulation. All
experiments containing the anchorage additive shows a stable
anchorage over time. The effect of the anchorage additive
overshadows the effect of SiH/SiVi ratio and of platinum catalyst
level.
COMPARATIVE EXAMPLES C3 TO C10
[0053] Examples 3 to 10 were repeated using the blend CBL in place
of the anchorage additive ARP used in Examples 3 to 10. The results
are shown in Table 4.
TABLE-US-00004 TABLE 4 Days at 65.degree. C./85% RH Example 0 1 4 6
12 30 C3 NNN VSRO VSRO NNN VSRO VSRO C4 VSRO NNN NNN NNN VSRO RO C5
NNN VSRO GRO GRO GRO GRO C6 NNN NNN NNN GRO GRO GRO C7 VSRO NNN NNN
NNN NNN NNN C8 NNN NNN NNN NNN NNN NNN C9 NNN GRO GRO GRO GRO GRO
C10 NNN NNN NNN NNN NNN NNN
[0054] Table 4 shows that when the cold blend of silanol-terminated
methylvinylsiloxane dimethylsiloxane copolymer and
glycidoxypropyltrimethoxysilane is used as anchorage additive, the
stability of the anchorage depends on several factors including the
SiH/SiVi ratio, platinum catalyst level and dwell time in the
curing oven. Some formulations do not show a stable anchorage even
with a high level of the blend CBL. Comparing Examples 3 to 10 to
Comparative Examples 3 to 10, the blend CBL is not as robust as the
reaction product anchorage additive ARP to maintain a high level of
aged anchorage regardless of the SiH/SiVi ratio, platinum catlyst
concentration and cure temperature/time.
EXAMPLE 11
[0055] 96.4% by weight of the trimethylsilyl,
vinyldimethylsilyl-terminated poly(dimethylsiloxane-silicate)
copolymer QBP of Example 1 was mixed with 0.6% ethynyl cyclohexanol
inhibitor and 3% of the anchorage additive ARP of Example 1. The
resulting blend was mixed with sufficient
poly(methylhydrogen)siloxane crosslinker MHS to give a SiH/Vi ratio
of 2.6:1 and sufficient catalyst CAT to give 120 ppm platinum.
[0056] After blending, the prepared release coating was coated on
`Jindar` PET film of 30 micron using 3 rolls reverse gravure
coating head at 18 m/min. It was cured for 30 sec at 150.degree. C.
After curing, a small part of the coating film was treated with
methylisobutyl ketone solvent and the amount of coating dissolved
(% extractables) was measured. The results are shown in Table 5
below.
[0057] BASF V210 acrylic emulsion adhesive was coated over the
cured silicone release coating using a bar coater and then dried at
150.degree. C. for 30 sec in a static oven. After drying, the
siliconised, adhesive coated film was laminated with 50 micron Mark
`Jindal 400` PET using a hot roll laminator. Two laminated samples
were aged in a humidity chamber at 50.degree. C./70% R.sup.H for 20
days and then at 65.degree. C./85% RH for 14 days. After this, the
anchorage was measured by rubbing off the silicone with a finger.
The results are shown in Table 5, using the same rating system as
in Example 1.
EXAMPLE 12
[0058] 80% by weight of a silanol-terminated methylvinylsiloxane
dimethylsiloxane copolymer of viscosity 20 centiStokes comprising
{acute over (.alpha.)},.omega.-hydroxy-terminated siloxane and
{acute over (.alpha.)}-hydroxy-.omega.-methoxy-terminated siloxane,
was reacted with 20% methyl(3-glycidoxypropyl)diethoxysilane in the
presence of potassium silanolate at 100.degree. C. for an hour to
produce a reaction product ARP2 containing at least one epoxy
group, at least one alkenyl group and at least one alkoxy group in
its molecule.
[0059] A release coating composition was prepared as described in
Example 11, using ARP2 as anchorage additive in place of ARP.
COMPARATIVE EXAMPLE C12
[0060] A release coating composition was prepared as described in
Example 11, using a cold blend of the silanol-terminated
methylvinylsiloxane dimethylsiloxane copolymer of Example 12 and
methyl(3-glycidoxypropyl)diethoxysilane in weight ratio 80:20 as
anchorage additive in place of ARP.
EXAMPLE 13
[0061] 50% by weight of a silanol-terminated methylvinylsiloxane
dimethylsiloxane copolymer of viscosity 20 mm.sup.2/s, comprising
{acute over (.alpha.)},.omega.-hydroxy-terminated siloxane and
{acute over (.alpha.)}-hydroxy-.omega.-methoxy-terminated siloxane,
was reacted with 50%
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane in the presence
of potassium silanolate at 100.degree. C. for an hour to produce a
reaction product ARP3 containing at least one epoxy group, at least
one alkenyl group and at least one alkoxy group in its
molecule.
[0062] A release coating composition was prepared as described in
Example 11, using ARP3 as anchorage additive in place of ARP.
COMPARATIVE EXAMPLE C13
[0063] A release coating composition was prepared as described in
Example 11, using a cold blend of the silanol-terminated
methylvinylsiloxane dimethylsiloxane copolymer of Example 13 and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane in weight ratio
50:50 as anchorage additive in place of ARP.
EXAMPLE 14
[0064] 45.5% by weight of a silanol-terminated methylvinylsiloxane
dimethylsiloxane copolymer of viscosity 20 mm.sup.2/s, comprising
{acute over (.alpha.)},.omega.-hydroxy-terminated siloxane and
{acute over (.alpha.)}-hydroxy-.OMEGA.-methoxy-terminated siloxane,
was reacted with 45.5% 3-glycidoxypropyltrimethoxysilane and 9%
methylvinyldimethoxysilane in the presence of potassium silanolate
at 100.degree. C. for an hour to produce a reaction product ARP4
containing at least one epoxy group, at least one alkenyl group and
at least one alkoxy group in its molecule.
[0065] A release coating composition was prepared as described in
Example 11, using ARP4 as anchorage additive in place of ARP.
[0066] The release coating compositions of Examples 12 to 14 and
Comparative Examples 12 and 13 were coated on PET film, cured and
tested for extractables as described in Example 11. The results are
shown in Table 5 below. The coated film was laminated and aged and
tested for anchorage as described in Example 11, and these results
are also shown in Table 5,
TABLE-US-00005 TABLE 5 Example No. % extractables Anchorage test
result 11 3.2 NNN 11 2.9 NNN C12 2.6 GRO C12 1.2 GRO 12 3.3 NNN 12
3.3 NNN C13 2.9 GRO C13 3.4 GRO 13 0.5 NNN 13 1.0 NNN 14 0.7 NNN 14
4.1 NNN
* * * * *